To present your Overflow diagram you have to click on the Present icon at the top right of the Editor or use CMD-Enter. From the Player you can exit back to the Editor by pressing ESC or the "Back to Editor" button.
Your presentation is auto-generated from your Overflow diagram. It is interactive in the sense that screens, images, and shapes become focal points and any element (or screen layer) that has an outgoing connector becomes active and can lead you to the destination element of that connector (upon clicking).
You can click to navigate to screens, images & shapes or on connectors to follow it up to its destination. Using the arrow keys will transition over to nearby elements in the specified direction.
A beautiful zoom-out - zoom-in transition while navigating makes this a captivating experience, while at the same time giving you and your audience a glimpse of the surrounding elements. You can turn this off if you like with Cmd + f.
To get a bird's-eye view of your Overflow diagram, you can press Cmd + 1.
You have several zoom options, as seen in the screenshot below.
You can navigate through your boards using the Boards menu on the left of the Player window, or Cmd + ↑ and Cmd + ↓
You also have the options (found in the Options menu) to start over, show/hide interaction hints, show/hide connectors, turn flight animation on/off, hide the Player UI and view keyboard shortcuts.
Another important feature of the Presentation mode is the Navigator map you can show and hide with 'N'. It appears at the top right corner and shows you your current viewport (in blue). It is also interactive: you can move the navigator's blue frame to change viewport.
Note: If you want to exclude an element from being active in the presentation (i.e. not be a focal point), you can choose the relevant option ("Set as Inactive") from the context menu in the Editor while having the particular element selected.